Apparatus for checking the quality of preforms each having a body made of plastics material

ABSTRACT

The apparatus is intended for performing quality checks on preforms ( 10 ) each having a body made of plastics material having an internal cavity ( 12 ) communicating with the exterior through an end opening ( 14 ) of the body. The apparatus comprises: a conveyor device ( 20 ) for transporting the preforms ( 10 ) along a predetermined path, an optical device ( 22 ) disposed along the path and suitable for forming an image of each of the preforms ( 10 ), a pneumatic device ( 24 ) disposed along the path and suitable for putting the internal cavity ( 12 ) of each of the preforms ( 10 ) under partial vacuum for a predetermined period of time, an electronic control unit ( 28 ) suitable for comparing the images of the preforms ( 10 ) with a standard reference image and/or for checking whether the value of the partial vacuum remains unchanged during the said period of time, and a selector device ( 26 ) disposed along the path and capable of separating the preforms ( 10 ) on the basis of the result of the comparison and/or checking operations performed by the control unit ( 28 ).

The present invention relates to apparatus for checking the quality ofpreforms each having a body made of plastics material having an internalcavity communicating with the exterior through an end opening of thebody.

These preforms are usually produced by injection moulding and areintended subsequently to be subjected to blowing in order to adopt thedesired final shape. A typical example of articles produced by thesetechniques is that of containers, in particular bottles, made of PET andhaving capacities which may vary from a few decilitres to severallitres.

The object of the present invention is to provide an apparatus which canperform quality checking on these preforms with great reliability and athigh speed.

According to the invention, this object is achieved by means ofapparatus and a corresponding method of operation which have thecharacteristics referred to specifically in the appended claims.

By virtue of the presence of both optical and pneumatic checking means,the apparatus of the invention can ascertain the presence of defects ofsubstantially all of the types which usually occur in preforms, such asincorrect dimensions, ovalization, lack of material, minute holes and/orflash at the injection point, annular burns, annular traces of moisture,non-fused spots, crystalline spots, the presence of foreign particlesand/or bubbles, and colour variations and streaks.

The use of the apparatus of the invention consequently prevents all ofthe problems that are brought about by the presence of one or more ofthe above-mentioned defects during subsequent processing stages as wellas during the handling and use of the finished product. In particular,emergency stoppages of the blowing and filling machines, precautionaryrejects by these machines, and the production of aesthetically and/orfunctionally unsatisfactory finished articles, are prevented.

Further advantages and characteristics of the present invention willbecome clear from the following detailed description which is providedby way of non-limiting example with reference to the appended drawings,in which:

FIG. 1 is an elevational view of a preform which can be checked by theapparatus of the invention,

FIG. 2 is an overall perspective view of the apparatus of the invention,

FIG. 3 is a schematic plan view of the apparatus of the invention,

FIG. 4 is a side elevational view showing some components of theapparatus of the invention, on an enlarged scale, and

FIG. 5 is a plan view showing some components of the apparatus of theinvention, on an enlarged scale.

The apparatus shown in FIGS. 2 to 5 can be used to perform qualitychecks on preforms 10 each having (FIG. 1) an oblong body made ofplastics material, typically PET. The body has an internal cavity 12communicating with the exterior through an end opening 14 which issurrounded by an annular collar 16 that projects from the outer surfaceof the body.

The apparatus comprises (FIGS. 2 and 3) a feed unit 18 for supplying thepreforms 10, a conveyor device 20 for transporting them along apredetermined path, an optical device 22, a pneumatic device 24, and aselector device 26 which are arranged along the path, and an electroniccontrol unit 28 suitable for receiving signals from the optical andpneumatic devices 22, 24, processing the signals, and consequentlycontrolling the selector device 26.

The feed unit 18 is of conventional type and enables the preforms 10,which are initially piled up loosely in a container 30, to be arrangedin a continuous row in which they are arranged vertically with theiropen ends 14 facing upwards.

Downstream of the feed unit 18 there is (FIGS. 4 and 5) an input member32 for introducing the preforms 10 into the conveyor device 20. Theinput member 32 is constructed in the form of a disc mounted forrotating about its own central axis 34 which is oriented vertically. Thedisc has on its periphery a plurality of spaced-apart seats 36 suitablefor supporting the collars 16 of respective preforms 10.

The conveyor device 20 is of the chain type, extends in an endlesscircuit in a horizontal plane, and has a drive motor 38. It has anoutward pass 40, a return pass 42, and a first end 44 and a second end46 at which the movement of the chain is reversed about respective axes48, So which are arranged vertically.

The conveyor device 20 further comprises a plurality of members 52 forthe selective gripping of respective preforms 10. Each member 52comprises a bar 54 which is arranged horizontally and is mounted so asto be movable along an axis substantially perpendicular to the axis ofmovement of the chain and which has resilient biasing means, inparticular a helical spring 56. Each bar 54 has a shaped gripping end 58which can clamp a preform 10 against a recessed seat 60 formed in thechain, and an opposite end 62 which acts as a follower and can interferewith a control member 64 which is arranged internally beside the endportion of the return pass 42 and the initial portion of the first end44 of the conveyor device 20. The plane in which the bars 54 of thegripping members 52 lie is disposed at a level slightly above that ofthe general plane of the disc of the input member 32.

The optical device 22 comprises a plurality of television cameras 66,68, 70, 72 and means 74 for illuminating the preforms 10, for example,one or more incandescent or fluorescent lamps arranged in the region ofthe outward pass 40 of the conveyor device 20. The first televisioncamera 66 is arranged beside the path so that its optical axisintersects the path substantially perpendicularly. The second and thirdtelevision cameras 68, 70 are arranged on opposite sides of the firsttelevision camera 66 so that their respective optical axes are inclinedat respective acute angles α, for example, of the order of 45°, to theoptical axis of the first television camera 66. Finally, the fourthtelevision camera 72 is disposed above the path defined by the conveyordevice 20.

The pneumatic device 24 comprises a carousel 76 mounted for rotatingabout its central axis 50 which is arranged vertically and coincideswith that of the second reversal end 46 of the conveyor device 20. Thecarousel 76 supports on its periphery a plurality of tubular rods 78mounted so as to be movable along axes parallel to the axis 50. Each rod78 has a longitudinal internal cavity 80 and a lower end provided with aclosure element 82 with a protuberance 84 with a rounded head having athrough-hole 86 which is connected to the cavity 78 and with which apressure sensor 88 is associated. Each rod 78 also has an open upper end90 which is connected by means of pipes 92 to suction means 94, such as,for example a suction pump. A pin 96 projects radially inwardly from thelateral surface of each rod 78 and extends into a corresponding groove98 formed on the outer surface of a stationary cylindrical body 100mounted coaxially around the axis 50 of the carousel 76.

The selector device 26 is disposed along the return pass 42 of theconveyor device 20, upstream of the control member 64. It comprises acam 102 mounted for rotating about a vertical axis 104 and havingsectors of different radial extent so that it can interfere selectivelywith the follower ends 62 of the bars 54 of the gripping members 54,according to its own angular positioning relative to the axis 104.

The apparatus described above operates as follows.

Each preform 10 supplied by the unit 18 is received individually in aseat 36 of the disc of the member 32 and is brought to the region of thefirst end 44 of the conveyor device 20 as a result of the rotation ofthe disc about its own axis 34. The gripping ends 58 of the bars 54approach the disc in an extended configuration as a result of theinterference which is created between the follower ends 62 and thecontrol member 64 and each gripping end 58 can thus encompass the neckof a respective preform 10 between its own internal surface and the seat60 of the chain facing that surface. As soon as the follower end 62 ofthe bar 54 of a given gripping member 52 is no longer in contact withthe control member 64 as a result of the movement of the conveyor device20, the spring 56 brings about retraction of the gripping end 58 whichthus clamps the preform 10 against the associated seat 60. The preform10 is thus loaded onto the conveyor device 20 and is carried towards theoptical device 22 by virtue of the movement of the conveyor.

The three television cameras 66, 68, 70, which frame each preform 10successively as it passes along the outward pass 40, can provide asubstantially complete image of the lateral surface of the preform 10,and the fourth television camera 72 can provide a plan view thereof.

These images are transmitted to the control unit 28 and are comparedwith a previously stored reference image of a standard preform. Thiscomparison is performed with the use of conventional software programmesand enables an assessment to be made as to whether or not a givenpreform 10 satisfies the required quality standards. In particular, thepresence of any abrupt spatial variations in the light reflection and/ortransmission levels, which indicate the presence of defects, is checked.In accordance with this assessment, the control unit 28 issues a commandwhich is executed at the moment at which the preform 10 passes theselector device 26. If desired, the control unit 28 can also emitwarning signals, for example, optical and/or acoustic signals, when thepresence of a defect is indicated.

The preform 10 which has been examined by the optical device 22 is thensent towards the pneumatic device 24 which is disposed in the region ofthe second end 46 of the conveyor device 20. Here, the rotation of thecarousel 76 brings about lowering of the rods 78, owing to theengagement of the pins 96 in a downwardly inclined portion of thecorresponding groove 98, so that the round-headed protuberances 84 whichclose their lower ends enter the open upper ends 14 of respectivepreforms 10.

When the lowering movement of a rod 78 has been completed and theprotuberance 84 is inserted in the open end 14 of the preform 10 in aleaktight manner, the suction means 94 are activated and produce adesired degree of vacuum in the cavity 12 of the preform 10 through thepipes 92, the tubular cavity 80, and the hole 86. If the preform is freeof defects, it remains under vacuum for the time taken by the preform 10and by the rod 78 associated therewith to rotate about the axis 50 untilthe pin 96 is engaged in an upwardly inclined portion of the groove 98and causes the rod 78 to be lifted and the protuberance 84 to bedisengaged from the open end 14 of the preform 10. During this period oftime, the sensor 88 measures the value of the pressure prevailing in thecavity 12 and transmits it to the control unit 28 which checks whetherthe vacuum value initially imposed has remained substantially unchanged.In this case again, on the basis of the outcome of this check, thecontrol unit 28 issues a command which will be executed at the momentwhen the preform 10 passes the selector device 26.

In detail, if at least one of this latter check and the comparisonpreviously performed between the image of the preform 10 produced by thetelevision cameras 66, 68, 70, 72 and a standard reference image hasgiven a negative result, the control unit 28 brings about a rotation ofthe cam 102 about its own axis 104 which causes it to interfere with thefollower end 62 of the gripping member 52 which engages the preform 10in question. The gripping end 58 of the bar 54 is thus moved away fromthe associated seat 60, with consequent disengagement of the preform 10which falls into a first, reject-collection container 106. In thisconnection, it should be noted that, if a particular preform 10 has notpassed the optical assessment, it is not necessary to place it underpartial vacuum when it passes through the pneumatic device 24, since itsrejection has already been decided upon.

If, however, the preform 10 has positively passed both the pneumaticcheck and the optical comparison, the control unit 28 does not bringabout a rotation of the cam 102. The movement of the gripping end 58 ofthe bar 54 away from the associated seat 60 therefore takes place onlywhen the follower end 62 interferes with the initial portion of thecontrol member 64 which is disposed beside the end portion of the returnpass 42 of the conveyor device 20. In this case, therefore, the preform10 falls into a second collecting container 108 and is destined forsubsequent blowing in order to adopt the desired final shape.

The apparatus described can check as many as 22,000 preforms per hour,irrespective of their type and size, and can detect defects ofdimensions even less than 0.35 mm when examining a region of 150 mm.

Naturally, the principle of the invention remaining the same, thedetails of construction and forms of embodiment may vary widely withrespect to those described purely by way of example, without therebydeparting from its scope. In particular, the apparatus of the inventioncould also be mounted immediately downstream of a preforminjection-moulding plant and could be supplied directly with thepreforms just moulded. In this case, the prompt detection of anyrepeating defects could enable the moulding parameters to be modified ingood time, thus limiting the number of preforms to be rejected.

Moreover, the arrangement of the optical and pneumatic devices could bethe reverse of that shown in the drawings, with consequent reversal ofthe order in which the respective checks are performed.

1. An apparatus for checking the quality of preforms (10) each having abody made of plastics material having an internal cavity (12)communicating with the exterior through an end opening (14) of the body,the apparatus comprising: a conveyor device (20) for transporting thepreforms (10) along a predetermined path, an optical device (22)disposed along the path and suitable for forming an image of each of thepreforms (10), a pneumatic device (24) disposed along the path andsuitable for putting the internal cavity (12) of each of the preforms(10) under partial vacuum for a predetermined period of time, anelectronic control unit (28) suitable for comparing the images of thepreforms (10) with a standard reference image and/or for checkingwhether the value of the partial vacuum remains unchanged during thesaid period of time, a selector device (26) disposed along the path andcapable of separating the preforms (10) on the basis of the result ofthe comparison and/or checking operations performed by the control unit(28), a carousel (76) mounted for rotating about its central axis (50)and supporting on its periphery a plurality of tubular rods (78) mountedso as to be movable along axes parallel to the axis (50), each rod (78)having a longitudinal internal cavity (80), a lower end provided with aclosure element (82) with a protuberance (84) with a rounded head havinga through-hole (86) which is connected to the cavity (80) and with whicha pressure sensor (88) is associated, and an upper open end (90) whichis connected to suction means (94) and in which a pin (96) projectsradially inwardly from the lateral surface of each rod (78) and extendsinto a corresponding groove (98) formed on the outer surface of astationary cylindrical body (100) mounted coaxially around the axis (50)of the carousel (76).
 2. An apparatus for checking the quality ofpreforms (10) each having a body made of plastics material having aninternal cavity (12) communicating with the exterior through an endopening (14) of the body, the apparatus comprising: a conveyor device(20) for transporting the preforms (10) along a predetermined path; anoptical device (22) disposed along the path and suitable for forming animage of each of the preforms (10); a pneumatic device (24) disposedalong the path and suitable for putting the internal cavity (12) of eachof the preforms (10) under partial vacuum for a predetermined period oftime, wherein the pneumatic device (24) comprises a carousel (76)mounted for rotating about its central axis (50) and supporting on itsperiphery a plurality of tubular rods (78) mounted so as to be movablealong axes parallel to the axis (50), each rod (78) having alongitudinal internal cavity (80), a lower end provided with a closureelement (82) with a protuberance (84) with a rounded head having athrough-hole (86) which is connected to the cavity (80) and with which apressure sensor (88) is associated, and an upper open end (90) which isconnected to suction means (94); an electronic control unit (28)suitable for comparing the images of the preforms (10) with a standardreference image and/or for checking whether the value of the partialvacuum remains unchanged during the said period of time; a selectordevice (26) disposed along the path and capable of separating thepreforms (10) on the basis of the result of the comparison and/orchecking operations performed by the control unit (28); and in which apin (96) projects radially inwardly from the lateral surface of each rod(78) and extends into a corresponding groove (98) formed on the outersurface of a stationary cylindrical body (100) mounted coaxially aroundthe axis (50) of the carousel (76).
 3. An apparatus for checking thequality of preforms (10) each having a body made of plastics materialhaving an internal cavity (12) communicating with the exterior throughan end opening (14) of the body, the apparatus comprising: a conveyordevice (20) for transporting the preforms (10) along a predeterminedpath, the conveyor device comprising a plurality of members (52) for theselective gripping of a respective preform (10), in which each of theselective gripping members (52) comprises a bar (54) mounted so as to bemovable along an axis substantially perpendicular to the axis ofmovement of the chain and provided with resilient biasing means, the bar(54) having a shaped gripping end (58) which can clamp a preform (10)against a recessed seat (60) formed in the chain and an end (62) whichacts as a follower and can interfere with a control member (64) disposedin the region of the end portion of a return pass (42) and of theinitial portion of the first end (44) of the conveyor device (20), inwhich the conveyor device (20) is a chain, extends in an endless circuitin a horizontal plane, has an outward pass (40), a return pass (42), anda first end and a second end (44, 46) at which the movement of the chainis reversed; an optical device (22) disposed along the path and suitablefor forming an image of each of the preforms (10); a pneumatic device(24) disposed along the path and suitable for putting the internalcavity (12) of each of the preforms (10) under partial vacuum for apredetermined period of time; an electronic control unit (28) suitablefor comparing the images of the preforms (10) with a standard referenceimage and/or for checking whether the value of the partial vacuumremains unchanged during the said period of time; a selector device (26)disposed along the path and capable of separating the preforms (10) onthe basis of the result of the comparison and/or checking operationsperformed by the control unit (28).
 4. The apparatus according to claim3 in which the selector device (26) is disposed upstream of the controlmember (64) and comprises a cam (102) mounted for rotating about avertical axis (104) and having sectors of different radial extent sothat it can interfere selectively with the follower ends (62) of thebars (54) according to its own angular position relative to the axis(104).